1. Field of the Invention
The present invention concerns metal materials of excellent corrosion resistance plated with a Zn-Mg alloy by vapor deposition, which are extremely useful as outer plates for vehicles or home electrical or electronic products, as well as various building materials. They include those materials that are used with or without coating, as well as include those materials used with or without fabrication such as in press molding.
Metal substrate materials to be plated in accordance with the present invention include Fe or Fe-based alloys, as well as non-iron metals such as Cu, Al and Ti or alloys thereof. They may be in any of shapes such as plates, corrugated, tubular or rod-like materials, as well as profiled materials H- or I-cross sectioned rods, with no particular restrictions. Although explanation is to be made hereinafter mainly for the most representative steel sheets, the technical scope of the present invention should not be construed only thereto.
2. Description of the Prior Art
Zn-plating has generally been employed as means for applying corrosion Resistant proof to steel sheets, etc. However, the demand for the improvement of the corrosion proofness of steel sheets, etc. has because increased, and Zn-plated steel sheets in the prior art can no more satisfy the requirement of users. It may be considered to improve the corrosion resistance by increasing the deposition amount of plating, but it brings about drawbacks such as powdering upon press molding, degradation upon spot welding and increased cost.
In view of the such a technical background, steel sheets plated with Zn-alloys such as Zn-Ni, Zn-Fe, Zn-Mn, Zn-Co, etc. utilizing the electroplating method have been developed, as well as steel sheets plated with multi-component Zn-Al alloys such as Zn-Al-Misch metal, Zn-Al-Si, Zn-Al-Mg, Zn-Al-Sn, etc. using the hot dip galvanizing method have also been developed.
However, for the Zn-alloy plated steel sheets obtained by the electroplating method, the following problems have been pointed out.